This application is submitted to fulfill requirements of the Special Dental Research Application program as described in NIH Guide Vol. 5 No. 20, Date 11-30-76. We plan to identify and characterize the genetic program for normal and pathological odontogenesis in the rat embryo dental organ. The molecular contributions of interacting dental epithelium and mesenchyme will be individually determined following developmental arrest in-vitro resultant from 5-bromodeoxyuridine (BrdU) treatment. Odontogenesis and organogenetic differentiation will be analyzed by morphologic, histologic, and biochemical criteria as measured in rat dental primordia grown in the absence and presence of a nontoxic, bioactive dose of BrdU. We plan as well to localize the distribution of bromouracil within epithelial and mesenchymal DNA nucleotide sequence elements. This information will be compared to the concurrent and simultaneous induction of a latent, endogenous type C RNA tumor virus elicited by the BrdU exposure. It is planned to specifically identify the germ layer source of the virus, as well as any potential molecular correlation between BrdU-mediated developmental arrest and simultaneous virogenic activation.